It is, the pivot positions aren't random but chosen strategical depending on the object. Wheels and things like airplane props have their pivot point at the center because developers might want to rotate and animate those, but walls all have them at the side of a 1 x 1 x 1 grid space to make sure you can quickly build structures. Sorry, a "change pivot" function isn't going to be added since it's technically impossible with the way models are saved.
Viewing post in Asset Forge 2.0 preview-1 now available! comments
Actually with new version the pivot seems to be the center of plane itself. So, if you place a cube 0.5 under the floor, the pivot will result central.
Anyway I forgot to congratulate you for the work. It took a while, but it was worth it. I hope the best for future updates and new customers! Keep it up! :-)